Gamma irradiation treatment of quince fruit (Cydonia oblonga Mill): effect on post-harvest retention of storage quality and inhibition of fungal decay

ABSTRACT Quince fruits harvested at commercial maturity were evaluated for using the feasibility of gamma irradiation to maintain storage quality and extend shelf-life. Matured green quince fruits were irradiated in the dose range of 0.3–2.1 kGy followed by storage under ambient (temperature 15 ± 2°C, RH 85%) conditions. The fruits were evaluated at intervals of 5 days for various physico-chemical parameters to investigate the effect. Studies revealed that irradiation treatment significantly (p ≤ 0.05) maintained the storage quality of quince fruit under ambient conditions. Positive correlations (r = 0.88) existed between the irradiation treatment and firmness retention, while as an inverse correlation (r = –0.89) existed between radiation treatment and water soluble pectin. Color scores of the fruits showed that extent of decrease in L value was 13.1% in control fruits compared to 3.4% and 2.8% in 1.8 kGy and 2.1 kGy irradiated fruits after 30 days of storage. Retention of higher hue values (79.8) in 2.1 kGy treated fruits indicated inhibition of chlorophyll degradation at higher doses. Microbial analysis indicated that in samples irradiated at 1.8 and 2.1 kGy, no microbial load was detected up to 15 days of ambient storage and resulted in about 2.4 log reduction in microbial load after 30 days of storage. Dose range of 1.8–2.1 kGy significantly inhibited the decaying of quince and resulted in about 40 days extension under ambient storage.


Introduction
Quince is a climacteric pome fruit belonging to Rosaceae family and is usually harvested during October-November (Sharma, Joshi, & Rana, 2011). Quince is considered as a rich source of health promoting and functional compounds which have potent hypoglycemic, anti-inflammatory, antimicrobial, anticancer, anti-allergic, antioxidant, and antiulcer action (Khoubnasabjafari & Jouyban, 2011;Koutb & Morsy, 2012;Légua et al., 2013;Oliveira et al., 2007;Rodríguez-Guisado et al., 2009;Silva & Oliveira, 2013;Szychowski, Munera-Picazo, Szumny, Carbonell-Barrachina, & Hernández, 2014;Wojdyło, Teleszko, & Oszmian´Ski, 2014). Quince fruit, due to its astringency and strong acidity, is not much appreciated for its fresh consumption and is mostly eaten after cooking or processed in to value-added products such as jam, jelly, candy, marmalade, and cakes (Mir et al., 2015;Silva et al., 2005). For processing purposes in to valueadded products, quince fruit therefore requires proper storage at 20°C, delay in ripening process and inhibition in mold growth to avoid losses and handle bulk quantity of the produce smoothly. Given the nutritional importance and functional properties of the fruit, strategies need to be developed for removing the constraints involved in the handling and storage of the quince for its smooth use as raw material in pharmaceutical and food industry (Alvarenga, Abrahao, Pio, Assis, & Oliveira, 2008;Pereira et al., 2011;Pio, Chagas, Barbosa, Signorini, & Del Aguila, 2009). The use of conventional chemicals as antiripening, anti-senescence, and microbial fumigants has been phased out and restricted throughout the world due to their adverse health effects and environmental issues (Cetinkaya, Ozyardimci, Denli, & Ic, 2006;Karabulut & Baykal, 2004). The adverse effects of these chemicals lower or limit the export capabilities of fresh as well as processed fruits. To overcome these adverse effects, quarantine barriers and at the same time extend the shelf-life, maintain storage quality of fresh fruits, and raise consumer confidence; alternate processes are needed.
One of the promising and effective alternative methods of processing and preserving the food products is the use of gamma irradiation (Bidawid, Farber, & Sattar, 2000;Temur & Osman, 2013). Irradiation has been recognized as an alternative to chemicals for treating fresh and dried agricultural products to overcome quarantine barriers in international trade, as a mode of decontamination, disinfestations, delaying the ripening and senescence of fruits and vegetables and for improving nutritional attributes and shelf-life (Hong et al., 2008;McDonald et al., 2012). A joint FAO/ IAEA/WHO Expert Committee on the wholesomeness of irradiated foods has ruled that foods subjected to low and medium dose of irradiation are safe and do not require toxicological testing (WHO, 1981).
Economic importance of the quince lies in the fact that its cultivation is expanding on a larger scale keeping in view its health beneficial effects which reflect the great potential of this fruit as raw material for food and pharmaceutical industries. The increase in its cultivation on commercial scale has resulted as a source of employment generation for the people involved in its trade. Review of the literature reveals that most of the studies conducted on quince fruit were aimed at evaluating the nutritional and proximate composition and natural variation in aroma profiles (Fiorentino et al., 2008;Koutb & Morsy, 2012;Leonel et al., 2016;Sharma et al., 2011;Silva et al., 2005). Few studies governing the effectiveness of gamma-irradiation treatment for pome fruits with respect to delay in ripening and senescence, control of fungal diseases during storage and insect infestation have also been conducted (Hussain, Meena, Dar, & Wani, 2010;Wani, Hussain, Meena, & Dar, 2008). However, to our best knowledge, no study has been conducted till date regarding the radiation processing of quince fruit. Therefore, the present study was conducted to determine the effect of gamma irradiation treatments on maintaining storage quality and shelflife extension of quince fruit grown in north India.

Raw material preparation
Quince fruits (Oblong variety) of uniform shape and size, firm texture, and proper maturity (180 d after full bloom) were procured from the quince orchards, Department of Horticulture, Habak, Kashmir. Selection of fruit was done from the same orchard. Fruit was pre-cooled by keeping at 2°C for 24 h in a cold storage chamber in order to remove field heat. The pre-cooled fruit was manually graded in order to have uniformity in size and any blemished or diseased fruits present were discarded followed by packing in cardboard boxes of size 0.5 m × 0.3 m × 0.3 m. Four boxes each containing 75 fruits spaced uniformly on cardboard trays were taken for each treatment including control.

Gamma irradiation treatment
The packaged fruit was subjected to gamma irradiation in the dose range of 0.3-2.1 kGy using PANBIT irradiator (Isotope Division, BARC, Mumbai, India) having Co-60 as the gamma-ray source. The fruits were irradiated at minimum dose rate of 145 Gy/h. To ensure uniformity of dose, boxes were turned by180°h alf way through the irradiation time and the over dose ratio (Dmax/Dmin) was determined and found to be 1.6. The dose rate was determined by Ceric-Cerous dosimetry. To ensure that fruit receives the exact dose, the dosimeters were placed in each fruit box for each treatment at high as well as low-dose spots. After completion of irradiation, fruits were kept under ambient (temperature 15 ± 2°C, RH85%) storage conditions for periodic evaluation of physico-chemical parameters namely firmness, titratable acidity, total sugars, ascorbic acid, chlorophyll content, total carotenoids, total phenols, polyphenol oxidase (PPO) activity, water soluble pectin (WSP), weight loss, percentage of full ripe fruits, decay percentage, color score, and microbial load as yeast and mold count.

Quality analysis
Objective color values on the surface of un-irradiated (control) and irradiated quince fruits were determined using a Hunter Colorimeter (Hunter Assoc, Reston, VA, USA;McGuire,1992). Color measurement were displayed in L (lightness), a (measure of browning) and b (yellowness) values. Hue and chroma were calculated from a and b values. Firmness of fruits was determined by hand pentrometer model 'FT-327' (EFFGI, Italy) provided with a 6 mm round plunger. Triplicate samples of 15 fruits were selected randomly and evaluated for firmness on four sides of each whole fruit and mean value was expressed in kg. The fruits initially used for firmness were subjected to juice extraction using an Omini mixer (Philips make). Total soluble solids (TSS) were determined at 20°C using ABEE refractometer model 'RSR-2' (Rajdhani Scientifics, India). Ten milliliters of juice was used for determining the acidity (% malic acid) as per the method of Ranganna (1986). Total sugars were determined by modifying the method of Miller (1959) using 3, 5-dinitrosalicylic acid reagent (DNSA). Chlorophyll was determined spectrophotometrically using the method of Witham, Blaydes, and Devlin (1971). For determination of total phenols, homogenized sample (10 g) of fruit in triplicates was extracted three times with 80% methanol. The extracts obtained were centrifuged for 20 min and the supernatants collected were dried under nitrogen. Total phenols were determined by Folin-Ciocalteu assay, which is an electron-transfer-based assay according to the method described by Waterhouse (2002). For determining polyphenol oxidase (PPO) activity, the quince samples were homogenized in a twofold amount of chilled 50 mM sodium phosphate buffer (pH 5.0) containing polyvinyl-polypyrrolidone (PVPP, 50g/l) for 2 min using a homogenizer (Philips, India). The homogenate was filtered through cheese cloth and the filtrate was centrifuged at 14,000 rpm for 30 min at 4°C. Activity of PPO enzyme from the crude enzyme extract was determined spectrophotometrically by measuring the increase in absorbance at 500 nm using L-tyrosine as substrate (Winder & Harris, 1991). Ascorbic and dehydroascorbic acid estimation was done by HPLC system of JASCO, Japan (model, LC-Net II/ADC), fitted with an automatic degassing unit, UV-2070 detector, PU-2080 pump and a HiQ-Sil C18 column (size 4.6 mm × 250 mm) using the method of Wimalasiri and Wills (1983).Total carotenoids as beta carotene equivalents were determined using the previously described method with slight modifications (Kimura & Rodriguez-Amaya, 2004). Loss in weight was determined by periodical weighing of samples. Water-soluble pectin was determined according to the method described by Ranganna (1986). Microbial load as yeast and mold count was determined by the serial dilution method using potato dextrose agar media (Aneja, 1996). Percentage of full ripe fruits and decay percentage was determined visually from known number of fruits. For each parameter, triplicate samples were used.

Statistical analysis
The data were analyzed statistically using completely randomized design experiment (Cochran & Cox, 1992). For each measurement, three replicates of samples were tested per treatment and mean ± standard deviation values were reported. Analysis of variance (ANOVA) of the data was performed using MINITAB statistical analysis software package (Minitab,version 11.12,32bit,Minitab (USA). Difference between means of data was compared by least significant difference (LSD) and Student's t-test was applied to determine if the difference was statistically significant. Differences at p ≤ 0.05 were considered to be statistically significant. Duncan's multiple range test was used to compare the mean values at each storage period. Coefficient of correlation was determined by Karl Pearson method.

Color scores
The primary criterion that the consumers consider about a product is its appearance. Color has been considered to have a key role in the choice of food, food preference, and acceptability, and may even influence taste thresholds, sweetness, perception, and pleasantness. Color is one of the main attributes, along with texture, that characterizes the freshness of most fruits (Rico, Martin-Diana, Barat, & Barry-Ryan, 2007b). Color scores of control and irradiated quince are depicted in Table 1. The statistical analysis of color score data revealed that no significant (p ≥ 0.05) difference existed among all color parameters for both control and irradiated quince fruits up to 5 days of storage except in L values which were significantly (p ≤ 0.05) higher in 2.1 kGy irradiated samples. L value has been used by several researchers as an indicator of deterioration (Kasim & Kasim, 2015). During storage, L values decreased in all the treatments and decrease was significantly (p ≤ 0.05) higher in control compared to samples irradiated at doses above 1.5 kGy. In samples irradiated in the dose range of 1.5-2.1 kGy, decrease in L values was statistically nonsignificant (p ≥ 0.05) up to first 15 days of storage. After the end of 30 days of storage, the extent of decrease in L value was 13.1% in control fruits compared to 3.4% and 2.8% in 1.8 kGy and 2.1 kGy irradiated fruits. The hue value, which represents true color and is considered as an effective parameter for visualizing the color appearance of food products also exhibited a decreasing trend during storage in all the treatments. The statistical analysis of the data indicated that decrease in hue values was marginally (p ≥ 0.05) different among treatments including control up to first 5 days of storage. After 15 days of storage, hue values were significantly (p ≤ 0.05) higher in fruits irradiated at 1.8 kGy and 2.1 kGy compared to all other treatments. After 30 days of storage, percentage decrease in hue value was 11.3% in control samples compared to 7.9% in 1.8 kGy and 7.3% in 2.1 kGy irradiated samples. The decrease in hue values indicates that color of quince fruits changed from green to light green-yelloworange as a result of chlorophyll degradation. Retention of higher hue values in 2.1 kGy treated fruits indicated inhibition of chlorophyll degradation at higher doses. The other color parameters namely a (browning/red index), b (yellowness index) and chroma recorded an increasing trend during storage in all the treatments including control. The increase in 'a', 'b' and chroma values was statistically nonsignificant (p ≥ 0.05) up to 5 days of storage in fruits irradiated at doses up to 1.5 kGy. On the other hand, in fruits irradiated at doses of 1.8 kGy and 2.1 kGy, the increase in 'a', 'b' and chroma values was statistically nonsignificant (p ≥ 0.05) up to 15 days of storage. After 30 days of storage, yellowness index increased by 43.3% in control and 20.9% in 2.1 kGy irradiated fruits. Chroma, which represents saturation of color either due to browning or chlorophyll degradation was significantly (p ≤ 0.05) higher in control fruits compared to irradiated ones. Data analysis pertaining to chroma indicated that enhancement in color saturation was statistically nonsignificant (p ≥ 0.05) up to 5 days in control and 0.3-1.5 kGy samples compared to 15 days in 1.8 kGy and 2.1 kGy fruits. Increase in chroma after the end of 30 days of storage was 46.3% in control compared to 23.0% in 2.1 kGy fruits. The changes in L and 'a' value were correlated with polyphenol oxidase activity (Kim, Kim, Smith, & Lee, 1995) whereas changes in 'b' value have been related to chlorophyll degradation (Kasim & Kasim, 2015). The ability of the radiation treatment (1.8-2.1 kGy) in maintaining the higher L and hue value and preventing the increase in b value and chroma is attributed to inhibitory effect of the treatment against the polyphenol oxidase activity and on chlorophyll degradation (Jang & Moon, 2011).

Firmness and water soluble pectin (WSP)
Effect of gamma irradiation treatment on firmness of quince fruit is shown in Figure 1(a). Data analysis indicated a nonsignificant (p ≥ 0.05) difference in firmness of control and irradiated quince fruits following irradiation (0 days). With advancement in storage, firmness recorded a decreasing trend in all the treatments including control. Statistical analysis of the data revealed that after 10 days of storage, there existed no significant (p ≥ 0.05) difference in firmness between control and 0.3-0.9 kGy irradiated samples. However, firmness of fruits irradiated between 1.2-2.1 kGy differed significantly (p ≤ 0.05) with respect to each other and was higher compared to control and 0.3-0.9 kGy irradiated samples. Data analysis also revealed that positive correlations (r = 0.88) existed between the irradiation doses and firmness thereby indicating that dose dependent retention in firmness was a general response of quince fruit to irradiation. 1.4 ± 0.4 a, 1 1.8 ± 0.4 a, 1 2.6 ± 0.3 b, 2 3.5 ± 0.5 b, 2 4.3 ± 0.5 b, 3 4.9 ± 0.6 b, 3 5.8 ± 0.5 d, 4 0.9 0.3 1.3 ± 0.5 a, 1 1.7 ± 0.4 a, 1 2.4 ± 0.3 b, 2 3.3 ± 0.4 b, 2 4.2 ± 0.4 b, 3 4.9 ± 0.5 b, 3 5.6 ± 0.3 d, 4 0.9 0.6 1.2 ± 0.4 a, 1 1.7 ± 0.5 a, 1 2.4 ± 0.4 b, 2 3.2 ± 0.5 b, 2 4.2 ± 0.6 b, 3 4.7 ± 0.3 b, 3 5.2 ± 0.4 c, 4 0.8 0.9 1.2 ± 0.4 a, 1 1.8 ± 0.4 a, 1 2.3 ± 0.5 a, 2 3.1 ± 0.5 a, 2 3.9 ± 0.6 b, 3 4.6 ± 0.5 b, 3 5. Values are mean ± SD (n = 3); LSD = least significant difference. Values within treatments in a column with different superscript lowercase letters (a-e) differ significantly (p ≤ 0.05) Values within storage periods in a row with different superscript numerical (1-5) differ significantly (p ≤ 0.05) After 20 days of storage, firmness of control and 0.3 kGy samples was marginally (p ≥ 0.05) different with respect to each other, where as firmness of all other irradiated samples differed significantly (p ≤ 0.05) with each other. This trend in firmness continued till 30 days of storage. After 30 days of storage, percentage decrease in firmness was 75.7% in control samples compared to 36.8-73.2% in 0.3-2.1 kGy irradiated samples. Among irradiated fruits, significant (p ≤ 0.05) retention in firmness (63.2%) was recorded in 2.1 kGy samples followed by 1.8 kGy samples (55.6%), respectively. Decrease in firmness is associated with the conversion of insoluble pectic fractions to the soluble forms during ripening. During ripening, the activities of enzymes namely protopectinase and pectin methylesterase responsible for hydrolyzing and solubilization of pectic substances increases, thereby contributing to firmness decrease. Since irradiation is known to delay the ripening and senescence of climacteric fruits; therefore, the significant retention of firmness in irradiated samples particularly those irradiated at doses above 1.5 kGy is attributed to the reduction in the enzymatic activity due to ripening delay as a result of radiation treatment (Hussain, Dar, & Wani, 2012). Effect of irradiation doses on water soluble pectin of quince fruit is shown in Figure 1(b). Data analysis indicated that no difference existed in WSP among treatments including control just after treatment (0 days of storage). During storage, WSP increased in all the treatments including control. Up to first 10 days, WSP of 0.3-0.9 kGy irradiated samples and control differed marginally (p ≥ 0.05) with respect to each other and was significantly (p ≤ 0.05) higher in comparison to the samples irradiated at dose above 1.2 kGy. After 15 days of storage, WSP of 1.5-2.1 kGy irradiated samples was significantly (p ≤ 0.05) lower compared to all other samples. Statistical analysis of the data revealed that among treatments, dose of 1.8 kGy and 2.1 kGy was significantly effective than all other treatments in inhibiting the increase in WSP of quince fruit during storage. Comparison of the data showed that after 30 days of storage, increase in WSP was 89.1% in control compared to 82.1% in 2.1 kGy irradiated fruits. Further our results showed existence of an inverse correlation (r = -0.89) between radiation treatment and WSP, thereby indicating an inhibitory effect of radiation treatment on the increase of WSP; thus confirming the higher (p ≤ 0.05) retention of firmness in irradiated 1.8 and 2.0 kGy samples.

TSS, total sugars, and titratable acidity
Effect of gamma irradiation treatment on the TSS and total sugars of quince fruit is shown in Table 2. Data analysis indicated that both TSS and total sugars of control and irradiated fruits differed marginally (p ≥ 0.05) at 0 days of storage; although the doses of 1.8 and 2.1 kGy resulted in a slight (p ≤ 0.05) increase in the values. During entire storage, both TSS and total sugars increased in all the treatments including the control; however increase was significantly (p ≤ 0.05) lower in samples irradiated at 1.8 and 2.1 kGy. It is also clear from the data that during first 5 days of storage, increase in TSS and total sugars was nonsignificant (p ≥ 0.05) in samples irradiated at doses above 0.9 kGy. Beyond 5 days of storage, the increase in TSS and total sugars was significant in all the treatments. Positive correlations existed between TSS and total sugars (r = 0.89) irrespective of treatments thereby indicating an increase in total sugars with increase in TSS. Close comparison of the data showed that TSS and total sugars of control and 0.3 kGy irradiated samples were nonsignificantly (p ≥ 0.05) different with respect to each other through out the storage. After the end of 30 days of storage, control samples recoded an increase of 64.1% in TSS and 75% in total sugars. On the other hand, irradiated 1.8 kGy and 2.1 kGy samples showed an increase of 55.6% and 54% in TSS and 66.9% and 65.7% in total sugars, respectively. The increase in TSS and total sugars is attributed to the enzymatic conversion of higher polysaccharides such as starches and pectins in to simple sugars during ripening. Since irradiation is known to delay the process of ripening and senescence and has an inhibitory effect on the activities of enzymes responsible for the conversion of higher polysaccharides in to simple sugars. Hence the higher doses of irradiation (1.8 and 2.1 kGy) were significantly (p ≤ 0.05) effective in maintaining the lower levels of TSS and total sugars, thus helped in delaying the ripening of the treated fruits (Hussain, Suradkar, Wani, & Dar, 2016). Data on titratable acidity indicated that fruits treated at doses of 1.8 and 2.1 kGy had significantly (p ≤ 0.05) higher acid values compared to other treatments including control just after treatment (0 days of storage). Acidity values of samples irradiated in the range of 0.3-1.5 kGy and control were marginally (p ≥ 0.05) different with respect to each other at 0 days of storage (Table 2). This trend in acidity among treatments continued up to 10 days of storage under ambient conditions. During first 5 days of storage, acid values decreased significantly (p ≤ 0.05) in samples irradiated in the range of 0.3-1.5 kGy; however, decrease was statistically nonsignificant (p ≥ 0.05) in control, 1.8 kGy and 2.1 kGy irradiated samples. After 15 days of storage, acid values were higher in samples treated with 1.2-2.1 kGy doses compared to other treatments including control. Beyond 20 days of storage, acid values of control and 0.3 kGy samples were marginally (p ≥ 0.05) different with respect to each other and significantly lower than all other treatments. Among treatments, dose range of 1.5-2.1 kGy was significantly (p ≤ 0.05) effective in maintaining the higher acid values of quince fruits toward the end of the storage. In control samples, decrease in acid values observed after 30 days of storage was 32.6% compared to 21.2% in 1.5 kGy and 20.4% in 1.8 kGy and 2.1 kGy samples, respectively. The loss in acid values during storage is largely due to the utilization of organic acid as respiratory substrates and as carbon skeleton for the 19.7 ± 0.12 c,5 21.7 ± 0.14 c,6 1.3 1.5 8.9 ± 0.11 a, 1 10.1 ± 0.12 b, 1 12.1 ± 0.14 b, 2 14.1 ± 0.21 b, 3 17.4 ± 0.21 c,4 19.1 ± 0.11 b,5 21.3 ± 0.14 c,6 1.3 1.8 9.1 ± 0.12 a, 1 9.8 ± 0.12 a, 1 11.8 ± 0.12 b, 2 13.8 ± 0.20 b, 3 16.8 ± 0.14 b,4 18.7 ± 0.13 b,5 20.5 ± 0.12 b,6 1.2 2.1 9.1 ± 0.11 a, 1 9.6 ± 0.12 a, 1 11.2 ± 0.12 a, 2 13.2 ± 0.21 a, 3 16.2 ± 0.14 a,4 18.1 ± 0.14 a, synthesis of new compounds during ripening. Also, accumulation of sugars during ripening contributes to decrease of acidity as a result of increase in TSS acid ratio. The retention of high acid values in samples irradiated at doses 1.5-2.1 kGy is an indication of delay in ripening effect of irradiation treatment (Wani et al., 2008).

Total chlorophyll and carotenoid content
Total chlorophyll content of control and irradiated quince fruits is shown in Table 3. Data analysis indicated that no significant (p ≥ 0.05) difference existed in chlorophyll content among control and irradiated fruits just after irradiation treatment. As the storage period advanced, degradation in chlorophyll content was observed in control as well as in irradiated fruits; however, in irradiated fruits decrease was dose dependent. After 5 days of storage, no significant difference existed in chlorophyll content of control and 0.3-1.5 kGy irradiated fruits and the values were significantly (p ≤ 0.05) lower compared to 1.8 and 2.1 kGy irradiated fruits. This trend in chlorophyll content continued up to 10 days of storage. After 15 days of storage, chlorophyll content of control and 0.3-0.9 kGy irradiated fruits was almost fully degraded and the contents were of the order of 1.6 ± 0.12 mg/100g in control and 2.2 ± 0.13 mg/100g in irradiated samples. On the other hand, the chlorophyll content of samples irradiated at doses above 0.9 kGy was significantly (p ≤ 0.05) higher and was in the range of 2.8 ± 0.21-6.5 ± 0.21 mg/100g after 10 days of storage. Data analysis revealed that after 15 days of storage, decrease in chlorophyll content was 83.2% in control, 70.8-78.4% in 0.3-1.2 kGy samples and 34.3-60.6% in 1.5-2.1 kGy fruits, respectively. No chlorophyll content was detected in control and 0.3-0.9 kGy irradiated fruits after 20 days of storage.
Our results revealed the existence of moderate positive correlation (r = 0.78) between chlorophyll retention and irradiation dose (0.3-1.2 kGy) and significantly positive correlation (r = 0.92) between chlorophyll retention and irradiation dose range of 1.8-2.1 kGy, respectively. After 30 days of storage, retention in chlorophyll content was 14.3% in 1.8 kGy samples compared to 26.3% in 2.1 kGy irradiated fruits. The loss of chlorophyll during storage is attributed to the change of chloroplasts into chromoplasts containing yellow and red pigments. The major loss of chlorophyll is mediated through an increase in the activity of the enzyme chlorophyllase during ripening which degrades the molecule. The retention of higher values of chlorophyll in case of samples irradiated in the dose range of 1.5-2.1 kGy can be attributed to the inhibitory effect of irradiation on the activity of chlorophyllase enzyme. Further, the free radicals produced .5 ± 0.12 a, 4 7.1 ± 0.14 a, 3 4.9 ± 0.16 a, 2 1.6 ± 0.12 a, 1 ND ND ND 1.5 0.3 9.7 ± 0.11 a, 4 7.4 ± 0.13 a, 3 5.3 ± 0.15 a, 2 2.1 ± 0.15 a, 1 ND ND ND 1.5 0.6 9.7 ± 0.12 a, 4 7.3 ± 0.14 a, 3 5.4 ± 0.22 a, 2 2.2 ± 0.17 a, 2 ND ND ND 1.4 0.9 9.5 ± 0.11 a, 4 7.6 ± 0.12 a, 3 5.6 ± 0.31 a, 2 2.2 ± 0.13 a, 1 ND ND ND 1.3 1.2 9.6 ± 0.13 a, 3 7.9 ± 0.15 a, 3 5.6 ± 0.32 a, 2 2.8 ± 0.21 b, 1 1.6 ± 0.23 a,1 ND ND 1.7 1.5 9.4 ± 0.15 a, 4 7.9 ± 0.22 a, 4 5.9 ± 0.21 b, 3 3.7 ± 0.24 c, 2 2.4 ± 0.24 a,1 1.1 ± 0.11 a,1 ND 1.5 1.8 9.8 ± 0.12 a, 4 8.4 ± 0.25 b, 4 6.6 ± 0.31 b, 3 5.1 ± 0.31 d, 2 3.9 ± 0.21 b,2 2.7 ± 0.15 b,1 1.4 ± 0.13 a,1 1.4 2.1 9.9 ± 0.14 a, 4 8.8 ± 0.24 b, 4 7.2 ± 0.21 b, 3 6.5 ± 0.21 e, 3 4.9 ± 0.22 c,2 3.7 ± 0.17 c,1 2.6 ± 0. during irradiation may act as stress signals and may trigger some stress responses resulting in slower degradation of chlorophyll (Fan & Thayer, 2001). Total carotenoid content of control and irradiated quince fruits in shown in Figure 1(c). Data analysis indicated no significant difference in carotenoid content among control and irradiated fruits just after treatment. During storage, carotenoids recorded an increasing trend and the increase was significantly (p ≤ 0.05) higher in control compared to irradiated samples. An inverse correlation (r = -0.87) existed between irradiation treatment and carotenoid accumulation, thereby indicating an inhibitory effect of radiation treatment particularly at doses above 1.2 kGy on the carotenoids accumulation. Up to first 5 days of storage, increase in carotenoids was statistically nonsignificant (p ≥ 0.05) in samples irradiated at doses above 0.9 kGy. This nonsignificant increasing trend continued in 1.2 kGy irradiated samples up to 10 days of storage compared to all other treatments, which exhibited a significant increase in carotenoids over the same storage period. Among treatments, beyond 20 days of storage; carotenoid content of control and 0.3 kGy irradiated samples differed nonsignificantly with respect to each other and the contents were significantly (p ≤ 0.05) higher compared to other treatments. After 30 days of storage, highest carotenoid content (17.4 ± 1.1 mg/100g) was recorded in control fruits, whereas lowest level was recorded in irradiated fruits particularly in 2.1 kGy irradiated samples (10.2 ± 0.71 mg/100g). This reduction in carotenoid accumulation in irradiated fruits is attributed to the ripening delay due to irradiation. Our results are consistent with recent study conducted by Silva-Sena et al. (2014) who reported a 30.0% decrease in the carotene content accumulation of irradiated papaya fruit Cv. Golden.

Total ascorbic acid
Effect of gamma irradiation treatment on ascorbic acid content of quince is shown in Table 3. The data reveal that ascorbic acid content of fruits treated with irradiation was marginally (p ≥ 0.05) lower compared to control at first day of storage. During storage, decrease in ascorbic acid was observed in all the treatments and the decrease was significantly (p ≤ 0.05) higher in control samples. Statistical analysis of the data also indicated that for all the storage periods, ascorbic acid content of control and 0.3 kGy irradiated samples was marginally (p ≥ 0.05) different with respect to each other but, significantly (p ≤ 0.05) lower compared to other treatments. Among treatments, after 5 days of storage; ascorbic acid content of the samples irradiated at doses above 0.9 kGy was significantly (p ≤ 0.05) higher compared to other treatments including control. However, after 15 days of storage, samples irradiated at doses above 1.2 kGy recorded higher ascorbic acid contents than rest of the treatments. This trend in ascorbic acid among treatments continued till end of the storage. After 30 days of storage, significantly (p ≤ 0.05) higher ascorbic acid content was retained in 1.2 kGy samples followed by 1.8 kGy samples, respectively. Percentage loss in ascorbic acid in quince fruit after 30 days of storage was 83.8% in control, 45.2% in 1.8 kGy samples and 38.2% in 2.1 kGy treated samples, respectively. Based on the results obtained, it can be inferred that major loss of ascorbic acid is because of storage rather than irradiation. The ascorbic acid loss during storage is known to be because of its antioxidant activity especially under postharvest storage conditions. However, lower ascorbic acid found just after irradiation, in fruits treated with 1.8 kGy and 2.1 kGy irradiation indicates that radiolysis could accelerate the conversion of ascorbic acid to dehydroascorbic acid (DHA). Similar changes in ascorbic acid content have also been reported by many authors during irradiation of whole and minimally processed fruits (Hussain, Suradkar, Wani, & Dar, 2015;Lee, Park, Lee, & Choi, 2003).

Weight loss
Effect of gamma irradiation on weight loss of quince fruits is shown in Figure 1(d). Data analysis revealed that weight loss increased during storage and was significantly higher in un-irradiated samples compared to irradiated samples. After 5 days of storage, weight loss was significantly (p ≤ 0.05) lower in samples irradiated at doses beyond 1.2 kGy. Data analysis also indicated that in samples irradiated at 1.2-2.1 kGy, increase in weight loss was statistically nonsignificant (p ≥ 0.05) up to 10 days of storage, whereas significant increase in weight loss was observed in control and other irradiated samples. After 15 days of storage, increase in weight loss was significant in all the treatments including control. Among treatments; beyond 25 days of storage, weight loss of control and 0.3 kGy samples differed nonsignificant (p ≥ 0.05) with respect to each other, and was significantly higher than other treatments. Results of the present study indicated the existence of inverse correlation (r = -0.88) between weight loss and irradiation treatment. Dose of 2.1 kGy irradiation proved to be significantly effective in reducing the weight loss through out the storage. Reduced weight loss of quince treated with irradiation is attributed to the inhibitory and delayed effects of the treatments on the physiological processes such as respiration and transpiration. Similar effects of irradiation treatment on the weight loss were observed in other horticultural products such as plum (Hussain et al., 2015). Therefore, reduction in weight loss due to irradiation will help in overcoming and preventing the quality deterioration in fresh horticultural crops after harvest.

Total phenols and polyphenol oxidase (PPO) activity
Total phenols of quince fruit treated with gamma irradiation are presented in Figure 2(a). The data plotted revealed that gamma irradiation at doses above 1.2 kGy caused a significant increase in total phenols of quince fruit just after the treatment compared to control fruits. Percentage increase of the order of 1.8-2.2% in total phenols was observed in samples treated with irradiation at dose range of 1.5-2.1 kGy just after treatment. The increase in total phenols in samples treated with irradiation is explained by the release of phenolic compounds from glycosidic compounds and degradation of larger phenolic compounds into smaller ones by irradiation (Krishnan et al., 2018). The increase in total phenols in fruits irradiated at dose range of 1.5-2.1 kGy was observed upto 5 days of storage. This increase in phenolics following irradiation has been attributed to the increase in phenylalanine ammonia lyase (PAL) activity; the key enzyme involved in the biosynthesis of phenolics, by gamma irradiation (Hussain et al., 2010;Oufedjikh, Mahrouz, Amiot, & Lacroix, 2000). With further advancement in storage, total phenols decreased in all the samples including control and the decrease was significantly higher in control and 0.3 kGy irradiated samples. In samples irradiated in the dose range of 0.9-1.5 kGy, decrease in total phenols was statistically nonsignificant up to 10 days of storage, beyond that total phenols recorded a significant decrease. Similarly, in samples irradiated at 1.8 kGy and 2.1 kGy, decrease in total phenols was marginal up to 15 days of storage, beyond that decrease was statistically (p ≤ 0.05) significant. Towards the end of the storage, treatment of 2.1 kGy was significantly (p ≤ 0.05) effective in maintaining higher levels of total phenols in quince fruit compared to all other irradiation doses. After 30 days of storage, control samples recorded a decrease of 12.3% in total phenols compared to 4.3% in 2.1 kGy irradiated samples. Decrease in total phenolics during storage is attributed to polyphenol oxidase (PPO) catalyzed oxidation of phenolic compounds. During storage, process of senescence, solubilization of cell wall pectic substances, and microbial infestation result in sub-cellular decompartmentation, disruption of membrane integrity and oxygen penetration, thereby leading to enhanced activity of PPO responsible for oxidation of phenols. It is usually believed that senescence or injury results in destruction of the biological barrier between PPO and polyphenols, and the enzyme is active only when it unites with its phenolic substrates. Moreover, quinines formed during PPO oxidation reactions may undergo redox recycling; thereby generate free radicals that are neutralized at the expense of phenols. Since irradiation has an inhibitory effect on the rates of respiration and senescence responsible for oxidative breakdown of phenolics, the treatment of irradiation was, therefore, able to retain the higher levels of total phenols in quince fruits toward the end of storage (Perez, Calderon, & Croci, 2007). The effect of gamma irradiation on PPO activity of quince fruit is shown in Figure 2(b). Data reveal that irradiation had a significant (p ≤ 0.05) effect on the inhibition of PPO activity in quince fruit. Prominent effect of radiation treatment on inhibition of PPO activity was observed at doses above 0.9 kGy. Statistical analysis revealed that irradiation treatment of quince in the dose range of 1.2-2.1 kGy resulted in 48.5-85.7% inhibition in PPO activity over control soon after the treatment. During storage, the PPO activity in quince fruits increased and the increase was significantly (p ≤ 0.05) lower in samples treated with gamma irradiation particularly at doses 1.5-2.1 kGy compared to control. In samples irradiated at 2.1 kGy, PPO activity increased nonsignificantly (p ≥ 0.05) up to first 10 days of storage, where as in all other treatments including control, significant increase in PPO activity was observed either just after treatment or 5 days of storage. Significant negative correlations (r = -0.96) existed between PPO activity and the treatments. Among the treatments, 2.1 kGy irradiation was significantly (p ≤ 0.05) effective in inhibiting the PPO activity up to 30 days of storage compared to other treatments. In irradiated samples; the inhibition in PPO activity after 30 days of storage over control was 42.2% in 2.1 kGy samples, 38.8% in 1.8 kGy samples and 24.3% in 1.5 kGy samples, respectively. The inhibition in PPO activity due to irradiation has proved significantly (p ≤ 0.05) beneficial in maintaining the higher levels of total phenols in quince fruits especially those irradiated at 1.8 and 2.1 kGy during storage.

Microbial load, percentage of full ripe fruits and decay
The decaying of quince fruit resulting from mold growth (Penicillium expansium) is a serious constraint during their storage and marketing and limits the standard shelf life of fruit to a maximum of 20 days under ambient conditions. The influence of radiation treatment on microbial load as yeast and mold count of quince fruit during ambient storage at 15 ± 2°C, RH 85% is shown in Table 3. Data pertaining to microbial load revealed that irradiation treatment above 0.9 kGy significantly (p ≤ 0.05) inhibited the yeast and mold count in fresh quince fruit. In samples irradiated at1.2 kGy, 1.5 kGy, 1.8 kGy and 2.1 kGy, no microbial load was detected up to 5 and 15 days of ambient storage, thereby resulting in around 3.8 and 4.9 log reductions in yeast and mold count after 5 and 15 days of storage. This beneficial effect of radiations at doses above 0.9 kGy in keeping the yeast and mold count below detection level up to 5 and 15 days of ambient storage is attributed to the radio-static effect of radiations, wherein cells become dormant upon exposure to radiations for extended period by virtue of radiation-induced reparable mutations. Once the damage is repaired, the cells then operate normally (Zhang, Zhaoxin, Fengxia, & Xiaomei, 2006). With further advancement in storage, the yeast and mold counts increased irrespective of treatment; however, the counts were lower in irradiated samples compared to control. After 30 days of storage, among treatments; dose of 2.1 kGy was significantly (p ≤ 0.05) effective in keeping the microbial load of quince fruits at very low levels and resulted in about 2.4 log reduction in microbial load over the 30 days of storage.
The results of percentage of full ripe fruits indicate that ripening was significantly (p ≤ 0.05) faster in control and 0.3 kGy irradiated samples. Irradiation treatment at doses of 1.8 kGy and 2.1 kGy was highly effective in delaying the ripening of quince fruits compared to other irradiation doses. The control unirradiated and 0.3 kGy irradiated samples were almost fully ripe after 18 days of storage. Samples irradiated in the dose range of 0.6-1.2 kGy were almost fully ripe within 21-27 days of ambient storage (Table 4). Quince fruits irradiated at 1.8 and 2.1 kGy were ripe up to the extent of 94.3% and 91.4% after 30 days of storage. After the fruits are fully ripe, they undergo senescence followed by decaying. Data on decay percentage indicated that under ambient conditions, control and 0.3 kGy irradiated samples started decaying after 20 days of storage and were almost fully decayed within 50 days. Among irradiation treatments, 1.2 and 1.5 kGy was effective in delaying the Values are mean±SD (n = 3); LSD = least significant difference (p ≤ 0.05); ND = no decay; FR = full ripe; FD = full decay; TF = total fruits Values within treatments in columns with different superscript lowercase letters (a-f) are significantly (p ≤ 0.05) different.
Values within storage periods in a row with different superscript numerical (1-7) are significantly (p ≤ 0.05) different.
decaying of quince fruits up to 25 days, whereas treatments of 1.8 and 2.1 kGy inhibited the decaying of fruits up to 35 days of storage. Irradiated 1.8 and 2.1 kGy fruits started decaying after 40 days and were decayed up to the extent of 54.3% and 48.6% within 60 days of storage, thereby indicating that 45.7% and 51.4% of these fruits were still in marketable condition. Thus, effect of gamma irradiation in delaying physiological processes and microbial proliferation responsible for decay has resulted in extended the shelf-life of quince fruits under ambient storage.

Cost benefit analysis of food irradiation
The cost of irradiating food is estimated at between 1.43 and 28.7 rupees per kilogram of the product. This wide range results from the many variables involved in any irradiation operation. Among the factors which affect the cost of irradiation are the dose of radiation employed (which can vary widely depending on the purpose of the treatment), the volume and type of product being irradiated, the type and efficiency of the radiation source, whether the facility handles one or a variety of food products, the cost of transporting food to and from the irradiator, special packaging of the food, and the cost of supplementary processing such as freezing or heating. The approximate cost required for construction of an irradiation plant large enough to permit economic operation is estimated in the range of rupees 10-12 crores excluding the land cost. However, based on the diverse application of technology, processing cost is quite inexpensive compared to other methods of preservation. Approximate costs of irradiation are in the range of rupees 0.50-1.0/kg of the produce for a low dose application such as sprout inhibition and rupees 3-5/kg for a high dose application such as treatment for microbial decontamination. The processing costs can further be brought down in a multipurpose facility by irradiating a variety of products throughout the year. Extension in shelflife of the produce also offsets the extra cost. Radiation processing can have a stabilizing effect of the market price of the product by reducing storage and distribution losses, improving the hygiene of food and increasing availability of the produce and avoiding market glut. Additional benefit of the processing to overcome quarantine barriers for export will further reduce the processing cost and will help in good market returns.

Conclusion
The present study revealed that gamma-irradiation treatment of quince proved significantly (p ≤ 0.05) beneficial in maintaining its storage quality and decreasing the microbial load. Among irradiation treatments, dose of 1.8 and 2.1 kGy proved significantly effective in keeping the yeast and mold count below detection levels up 15 days of ambient storage. Therefore, based on the results, it is concluded that post harvest radiation processing of quince at 1.8 and 2.1 kGy resulted in extension of 40 days in shelf life and can be used as potential alternative to chemical preservation of fresh quince. The extension in shelf life through gamma irradiation will help in overcoming the constraints involved in the handling and storage of the quince for its use in pharmaceutical and food industry.

Disclosure statement
No potential conflict of interest was reported by the authors.